1. Field of Invention
The instant invention relates to a drawing frame to draw fiber slivers with drawing rollers constituting pre-drawing and main drawing roller pairs and power transmission means to drive said drawing rollers as well as a sliver discharge mechanism.
2. Background of Art
The utilization of drawing rollers with two or more pairs of rollers to draw fiber slivers is known. The circumferential speed of the pairs of rollers increases from the inlet of the drawing frame to the outlet of the drawing frame. The lower roller of the roller pairs is driven by toothed wheels or toothed belts so to produce the slippage-free operation which is absolutely necessary for orderly drawing of the fiber slivers. The upper rollers are pressed against the lower rollers and the rollers thus clamp the fiber material running through between them.
It has been shown that toothed-wheel drives as well as toothed-belt drives of the drawing frame rollers have a detrimental effect upon the uniformity of fiber sliver drawing.
With toothed-wheel drives the clearance which exists between the individual teeth of the toothed wheels causes the roller pairs not to be driven simultaneously but one after the other, especially during run-up of the drawing-frame. This produces irregularities in the drawing of the fiber sliver.
DE-OS 20 44 996 proposes driving the drawing rollers via toothed belts. When such drives are used it was found that the accumulation of dirt between the teeth of the drive and deflection wheels over which the toothed belts are guided, as well as between the teeth of the toothed belt, cause irregular rotational movements of the drawing frame rollers to be produced. These irregularities lead to interference in the drawing of the fiber sliver as well as to increased wear of the drive elements. Especially where small toothed wheels are used and with toothed belts with small tooth divisions, such as are required for predrawing rollers because of the limited space available, soiling of the tooth clearances has a very detrimental effect. Manual cleaning of drive and deflection wheels as well as of the toothed belts is time consuming.
In addition to dirt, the oscillating characteristics of the drive means at the constantly increasing drawing speeds seriously impair the uniformity of fiber sliver drawing. Toothed-belt drives have unfavorable oscillating characteristics at high predrawing speeds.